New York Geothermal Open loop System Lockout

As we were all scratching our heads.. apparently knocked discharge temp down enough to throw the rest out of line.? Thermistor was checked as was line temp, flow was verified with buckets etc. System was my own so many evenings after work info was gathered/checked. wf was going to fly a tech out until he said he had seen the issue before.. I changed to a closed loop and it's been trouble free ever since. Have not seen the problem on any installs after that either, though I don't know of any with all the same scenarios needed to make it happen until reading this. Not sure if it's the same problem with the wtw unit but it sure sounds similar.

 

If your EWT is around 48For above, which I will be in Michigan, there is not much of another way the reduce your discharge temp on the water source side than not having enough flow. Yes, changing to closed loop with antifreeze and setting the antifreeze jumper to 15 F would solve the problem.
If your refrigerant level is fine, and the thermistor is ok, it comes down to flow...

 

47 degree ewt. Refrigerant level checked via pressures, superheat, subcool, all within specs. Flow at 15 gpm on open loop 4 ton, quite plenty I'd say, verified w 5gallon buckets n stopwatch. Brand new unit at the time,( no fouled coax) wf 4 t envision. So there must be a way. Not sure which unit you have doc but you could try this, hook up a hose from pressure tank to your flush valve for desuperheater, run the 48 degree water thru the dsh while monitoring the line temp at fp thermistor and see if it doesn't drop below 30 degrees. We could compare notes..

 

With 15 gpm, which is way too much flow for a 4 ton open system, your discharge temp would be around 43F. So let the DSH come on with cold water influx, which is less than 10 percent of total capacity, .....it does not cause fp1 to drop below 30F.

 

Does Not?.. or would be desired not?.. I say it Does. Yes. 15 gpm was for testing purposes only to rule out flow/ ice. So today I took the opportunity to flush my dsh coil, change filter, etc. and decided to see if I could awake the sleeping monster. When I changed to a closed loop I left the piping hooked up so by flipping a few switches and opening/closing some valves I can convert back to open loop. This time I rolled with 10 gpm, put temp clamps on line at fp1, ran unit in stg 2 with steady temps of 47 ewt, 40.3 lwt and a line temp of 38 deg. Hose from pressure tank to dsh in, dsh out to sump pit. After 5-10 min of run time opened valve to dsh, within 1 min line temp dropped to 23 degrees and guess what.. unit shut down on freeze protection with lwt barely changing. After almost 8 yrs it's still there! Set back to closed loop w 36 deg ewt, line temp of 32.5 deg and opened valve. Line temp dropped to 20 deg. Location of temp clamp and fp1 thermistor on this unit is between txv and source coax. So can we say outside of design or perhaps testing?

 

Back to the OP, it seems the solution may lie in the tank temp control setup. The critical water temp on my system was 55 deg, granted it was on the desuperheater but could a low load temp not cause the same issue as they both are on the hot gas side?

 

I did say it does not. I have to get my head around this here. What is your model number? The DSH has such a small impact (less than 10%) on the capacity, as indicated by almost no change in the LWT. It usually stays very close to the LWT, as you indicate, 40.3 LWT and 38 line temp, which is why it is used to determine the need for breeze protection. Give me you model number and let me get my head around this.

We run many WF HP on open loops with DSH.
I just checked one of it. This is with the DSh running.
EWT is 54, LWT is 47, Line temp is around 40F, again with DSH running.

 

NDV049A111NTR My line temp also remained steady when I returned the dsh back to service using the warm preheat tank water. It's when the dsh ewt is say below 60ish when it drops.

 

https://www.geoexchange.org/forum/attachments/screen-shot-2017-03-03-at-4-15-16-pm-png.2188/

Doc, this is a great pictorial of the heating/refrigeration cycle.
Couple Q's:
1- What is EAH?
2- The HE/HR ratio seems odd. Can you confirm?

Thanks.